Abstract: During the drilling and production of HTHP (high temperature and high pressure) well, its safety is seriously influenced by the annulus trap pressure which is induced by the closed annulus fluid due to thermal expansion. And the annulus trap pressure is in close relation with the closed annulus volume change. In order to analyze the effect of the deformation of casing cementing section on the annulus trap pressure, a casing-cement sheath-strata compatible deformation model was established according to the elastic deformation theory. Then, a multi-string annulus trap pressure calculation model was developed by analyzing annulus fluid parameters and casing deformation comprehensively. Finally, a case study was carried out to analyze the influence laws of casing deformation on annulus trap pressure. It is shown that when the deformation of casing cementing section is taken into account, the predicted annulus trap pressure is 13% lower and it is closer to the field measurement. This research plays an important and practical role in guiding the casing string design and safe production of HTHP wells.